Flow line systems which transport potentially dangerous fluids, such as anhydrous ammonia, commonly include a separable connection for emergency interruption of the flow line which extends between a stationary vessel and a potentially portable vessel, such as a transport vehicle. Occasionally, the driver of the transport vehicle inadvertently pulls away from the stationary vessel prior to disconnecting the flexible flow line, and the absence of a separable connection may otherwise cause a rupture of the fill line. The monetary loss of fluid from such a rupture is nominal compared to the danger of releasing toxic vapors. The release of anhydrous ammonia may seriously injure the operator, causing blindness, skin burns, or loss of smell. For other potentially dangerous fluids, such as propane and liquid petroleum gas, the release of the fluid may cause adverse environmental consequences to the filling station site or create a fire hazard. One type of improved breakaway connection, marketed as TRIPOD (TM) coupling, is disclosed in U.S. Pat. Nos. 5,228,474 and 5,320,133. The TRIPOD coupling is particularly suitable for positioning between a stationary filling platform and a transport vehicle.
In a typical anhydrous ammonia application system, a nurse tank, which may be periodically filled by the above-described transport vehicle, is attached to anhydrous ammonia applicator with a mechanical hitch. Each end of the hose which connects the nurse tank and an applicator includes a shutoff valve. A breakaway coupling is provided between the shutoff valves, and is designed so that it will uncouple with a pull force sufficiently small to not damage the nurse tank. The primary purpose of the breakaway coupling is both to separate or breakaway and to shut off the flow of ammonia in the event of separation of the applicator and nurse tank at the mechanical hitch.
The PIONEER (TM) breakaway coupling, used in anhydrous ammonia application systems, is distributed by Parker Hannifin Corporation. When disconnected, poppet valves in each half of the coupling are closed by respective valve springs, thereby stopping the flow of ammonia to the atmosphere. When the coupling is either fully connected or fully disconnected, a spring positions a sleeve to prevent locking balls from rising up out of their ball holes. When fully connected, the poppet valves in both coupling halves are open to allow ammonia flow. When the axial pull on the male coupling half exceeds the force of the sleeve spring, the coupling male half will pull out of the socket. The poppet valve then springs closed to stop the discharge of anhydrous ammonia from the flexible flow lines. The PIONEER coupler has been manufactured with stainless steel components which alleviated many of the problems it had with corrosion which led to failures in operation. There are, however, other characteristics inherent to this design.
The first and most significant problem with the PIONEER coupler is the flow restriction caused by the spring loaded poppets positioned in the flow stream. In anhydrous ammonia applications, the flow rate achievable through the breakaway coupler is of paramount importance. In situations where a farmer desires to put a certain amount of anhydrous ammonia per acre on a field, the time required to do the job is directly affected by the flow rate the application system can deliver. Anhydrous ammonia is typically not pumped to the application system but rather is driven solely by the fluid pressure of the anhydrous ammonia nurse (supply) tank. The pressure in the tank is a function of the ambient temperature, and when the temperature is relatively cool the tank pressure will be low. It is generally desirable to apply anhydrous ammonia when the ground is cool so as to improve absorption into the soil and minimize loss due to evaporation.
When the anhydrous ammonia meets a restriction in the application system, a pressure drop occurs, decreasing the maximum deliverable flow rate of the system. It is generally recognized that the breakaway coupler causes the most severe restriction in the system. When a farmer has several thousand acres to fertilize and there is a short time window where the soil temperature and moisture content is ideal for anhydrous application, it makes a big difference whether the application instrument can travel at, for example, 7 miles per hour and still achieve the desired application rate, or whether the speed must be reduced to, for example, 4 miles per hour because the system cannot deliver the flow required to run at 7 miles per hour. The difference can amount to additional days required to do the job. Because of these factors, a high flow breakaway coupler has always been desired.
A further problem with existing locking ball couplers is the difficulty of manually coupling or uncoupling them. This is routinely required for periodic safety inspection of the coupler or removal of the application hose for off-season storage. Existing devices require the user to muscle the coupler by hand to compress the main latch spring which typically requires from 200 to 300 pounds of force. The manual application of that level of force to a flexibly mounted coupler is at best difficult and at worst dangerous to do.
Other devices of interest are disclosed in U.S. Pat. Nos. 5,947,142, 5,699,822, 5,419,354, and 4,090,524. U.S. Pat. No. 5,947,142 discloses an improved breakaway coupling utilizing poppet-type valves. U.S. Pat. No. 5,699,822 discloses a breakaway coupling device using shear pins to couple male and female members and optionally including flapper-type valves. U.S. Pat. No. 5,419,354 discloses a frangible connector apparatus for controlling a fluid passage, providing at least one sliding gate movable transversely to the fluid passage. U.S. Pat. No. 4,090,524 discloses a valved fitting for handling flowing fluids having another valved fitting or conduit attached thereto wherein a frangible interconnection is utilized. Upon the frangible connection fracturing, such action is sensed by valve operating means for closing the valve against fluid flow producing a self-sealing fitting. A flapper valve is utilized to seal the valve passage with the goal of maximizing flow characteristics with a minimum of resistance during fluid flow.